The present invention relates to an acceleration sensor chip package.
Recently, technology for producing a microstructure having a size of a few hundred microns has been advanced using micro-machining technology based on semiconductor manufacturing technology. The technology has been applied to various sensors, for example, photo-switches in an optical communication system, and radio frequency (RF) components. Since such a microstructure can be produced with a conventional semiconductor manufacturing process, it is possible to mount a large number of microstructures on a single chip.
Such a chip formed of the microstructures having a system with a specific function is called Micro-Electrical-Mechanical-Systems (MEMS) or Micro-System-Technology (MIST; referred to as an MEMS device hereinafter). The MEMS device includes an acceleration sensor (see Patent Reference 1).    Patent Reference 1: Japanese Patent Publication No. 11-135804
In Patent Reference 1, the acceleration sensor is a piezo-type, and has a frame portion formed of a center portion and a beam portion. The beam portion extends at least between a portion of an inner circumferential side surface of the frame portion and the center portion. A weight portion (movable portion) is supported on the center portion to be freely movable. A supporting portion is provided for supporting a lower surface of the frame portion, and surrounds an outer circumferential edge of the weight portion through a cut portion thereof. The movable portion is integrated with the frame portion to form a microstructure, and moves upon receiving an external force. The frame portion has a small thickness and a small width. Such a sensor chip is generally formed as a packaged device.
With reference to FIGS. 16(A) and 16(B), a conventional acceleration sensor chip package will be explained. FIG. 16(A) is a schematic plan view showing the conventional acceleration sensor chip package viewed from an upper surface side for explaining constituents. An upper surface of a protection cover (described later) is omitted to provide a transparent view for showing an internal configuration. FIG. 16(B) is a schematic sectional view taken along a projected line 16(B)-16(B) in FIG. 16(A).
As shown in FIG. 16(A), a conventional acceleration sensor chip package 100 is provided with an acceleration sensor chip 110. The acceleration sensor chip 110 is provided with electrode pads 112 for outputting a signal from the acceleration sensor chip 110 or inputting a signal to the acceleration sensor chip 110. The acceleration sensor chip 110 is also provided with a movable structure 114 operating mechanically, and a sealing substrate 116 for sealing the movable structure 114 to regulate a movement thereof. As shown in FIG. 16(B), the sealing substrate 116 is attached to a substrate 120 with an adhesive 122.
An edge of an opening of a protection cover 130 is attached to the substrate 120, so that the protection cover 130 forms a closed space 140 for sealing the acceleration sensor chip 110. Outer terminals 150 are disposed at an edge of the substrate 120, and extend outwardly from inside the closed space 140 formed by the protection cover 130. In the closed space 140, the outer terminals 150 are electrically connected to the electrode pads 120 of the acceleration sensor chip 110 through bonding wires 160.
In the conventional acceleration sensor chip package described above, the acceleration sensor chip is electrically connected to the outer terminals through the bonding wires. The protection cover is provided for sealing the acceleration sensor chip while retaining the bonding wires. Accordingly, it is difficult to seal the acceleration sensor chip through transfer molding or potting using a liquid resin, thereby increasing a size of the acceleration sensor chip package.
Further, when the conventional acceleration sensor chip package is produced, the acceleration sensor chip is packaged after dicing. Accordingly, a cut waste may stick to an area around the movable portion (weight) upon dicing, so that the movable portion may be damaged and not operate properly.
In view of the problems described above, an object of the present invention is to provide an acceleration sensor chip package having a small size. Further, an object of the present invention is to provide a method of producing an acceleration sensor chip package in a simple process while preventing a movable portion from being damaged, thereby increasing a product yield.
Further objects and advantages of the invention will be apparent from the following description of the invention.